[CMake] checking arguments

[Andrea Crotti]

I find not so nice that CMake doesn't complain at all if some variables 
are not defined.
Is there a way to make it complain if a variable used is actually blank?

In the meanwhile I ended up with this:

set(COMPULSORY_ARGUMENTS PSI)
set(OPTIONAL_ARGUMENTS WORKSPACE CONTAINER_PATHS)

macro (check_compulsory_variable var)
   if (NOT DEFINED ${var})
     message(FATAL_ERROR "variable ${var} is not defined")
   endif ()
endmacro ()

macro (check_optional_variable var)
   if (NOT DEFINED ${var})
     message(WARNING "variable ${var} is not defined")
   endif ()
endmacro ()

foreach (arg ${COMPULSORY_ARGUMENTS})
   check_compulsory_variable(${arg})
endforeach ()

foreach (arg ${OPTIONAL_ARGUMENTS})
   check_optional_variable(${arg})
endforeach ()


which is not great but it does the job.
Any better solutions?